Better Accuracy with New Dexcom G4 Algorithm (and the Path Ahead)

Written by Mike Hoskins
| Published on November 18, 2014

I'm paying super-close attention to my Dexcom CGM (continuous glucose monitor) these days, and not just because I'm a Nightscout Newbie. Nope, ten days ago I also upgraded my Dexcom to the new "advanced algorithm" that supposedly makes the unit more accurate.

News of this advanced algorithm came in a press release Nov. 6, coincidentally the same day as the Dexcom quarterly earnings call, but the FDA had actually approved the new software update on Oct. 21. According to the announcement:

"The new Software 505 features the same advanced algorithm as used in artificial pancreas research around the world. The software will impact the performance of the Dexcom G4 ... already considered the most accurate CGM system on the market today. The software will be made available free of charge to adult patients using the Dexcom G4."

Lots of us Dexcom users in the diabetes community were pretty excited to hear this. But then we started asking ourselves (and each other): So, what does this new algorithm do, exactly?

Dexcom won't disclose details of how the new algorithm calculates differently, uttering that dreaded word "proprietary" when asked how the new software does the job better than before. But Dexcom's Executive VP of Strategy and Corporate Development Steve Pacelli says it wouldn't be far off to assume the algorithm "reduces some of the noise interference" in how the system communicates glucose sensor data. He tells us a majority of the CGM performance difference can be seen on the first day of use, and overall the most noticeable differences in accuracy should be seen when catching hypos and when blood sugars change rapidly.

A Great MARD

What we do know is that this technology is what's used in most of the artificial pancreas trials in which Dexcom's involved (it is indeed the CGM used in a majority of the AP trials going on out there). Accuracy of these glucose measuring devices is gauged using a standard measure called mean absolute relative difference (MARD), and the lower the result, the higher the accuracy. And yes! Dexcom's new algorithm scores much lower than anything we've seen -- the first single-digit MARD of 9.0%, compared to 13% in the previous G4 algorithm.

This is also a huge leap from the past 16% MARD score on Dexcom's Seven Plus, and from the competing Medtronic Enlite sensor, which scores between 13 and 17% depending on which studies you believe. Some PWDs also regularly compare contemporary sensors with the now-defunct Freestyle Navigator CGM, which had a MARD of about 12%.

So yes, this new G4 is the most accurate to date -- especially on the hypo side of the range -- and it's the closest we've come to fingersticks that have a MARD of about 5.6%.

What makes this update even more important is that it's part of Dexcom's bigger game plan -- namely, to get CGM results to the level where they're good enough to be FDA approved for use in dosing insulin. It's the dream of replacing fingersticks for real -- with labeling on the CGM saying it's approved for stand-alone use.

This isn't official yet, though some of us CGM'ers probably do use the continuous readings to make dosing decisions -- hoping for a day when the CGM becomes accurate enough to reduce the number of fingersticks required, and eventually replace them completely.

In these days of high test strip costs and scattered Medicare coverage for CGMs because they're considered "supplemental" devices, this labeling would be a huge boost on both fronts.

Getting Upgraded

Meanwhile, all new G4 receivers being sent out have the upgrade built in, and existing customers are invited to download the Software 505 upgrade online from the Dexcom site. You just plug in your receiver and click to update the firmware inside.

And what have I seen since upgrading my own system? Yep, my beloved CGM does seem to be more accurate and responding more quickly to my blood sugar changes -- especially in the low range. I've also noticed my G4 receiver reflects more dramatically the shifts in blood sugar, more immediately letting me know when these big jumps or drops happen instead of delaying the changes and making them appear more gradual trends.

But unfortunately, on the higher end of the BG spectrum, I'm noticing my results do seem skewed more often and way off from what my meter's showing. This is especially true when it's time to calibrate, and the readings have been 100+ points off. That's a little unnerving for me, as it's not been the case before this update.

Anyhow, it seems I'm not alone. I've seen several people commenting that it's more accurate on that lower end, though some have also reported more fluctuations and quicker arrow changes than before. And others have just not noticed any difference. As with everything in D, your sensor performance may vary.

Here's what we heard from one fellow D-peep Scott Powell in Ohio, who's been type 1 since 1981 and has been using the Dexcom G4 for several years since his Abbott Navigator CGM (no longer available in the U.S.) died.

"Overall I do think the Dexcom 505 software is more accurate. I've only had one or two tests since I updated that were > 10% error. That's much improved over the previous software. Still, I don't think it's as accurate as the Navigator was, but seems to be a definite step in the right direction."

Not Yet for Kids

Note to the wise: this algorithm update is not yet approved for pediatric use! That is, G4 was approved in February for use in kids up to age 17, but the FDA will have to approve any changes to those units separately. Dexcom says that's going to happen by end of the year, which is pretty soon. But in the meantime, anyone with a pediatric version of the G4 (it says so on the back and you get some kid-specific warnings) will have to use the older version of the algorithm. Not all kids are in this boat, as some may have "off-label" adult G4s if their docs were willing to prescribe the CGM before the new FDA approval came down.

Future Pump Issues

On top of that, two new pumps that will integrate the Dexcom CGM that are undergoing FDA review now won't be compatible with this new algorithm: the future Animas Vibe G4 and Tandem t:slim G4 devices, both slated to likely hit the market sometime in the next year or so, won't have the better-performing CGM algorithm. Ugh...

As Dexcom's Pacelli tells us that it's not just a matter of FDA filings based on the older tech; it's an issue built into the integrated insulin pumps. Neither the t:slim G4 nor the Animas Vibe will have the ability to support the new sensor algorithm.

Some science-savvy folks in the online community speculate it's probably because of how the pumps are built -- the t:slim G4's architecture has a built-in USB port that probably limits the newer software, while the the Animas Vibe actually uses an old-school IR port that wouldn't allow for the device to update the algorithm.

As a result, Pacelli tells us t:slimmers and Animas pumpers who get either integrated pump will either have to buy a separate Dexcom G4 receiver to have the advanced algorithm or they'll have to wait for the second generation of these integrated devices that will include the yet-to-be-filed G5 sensor.

Dexcom still plans to submit that next-generation G5 device for FDA review in the coming months, either by end of 2014 or early 2015. That transmitter will likely be the same as the G4 with this new AP algorithm built in, but the unit will talk directly to a smartphone, eliminating the need for a receiver.

Pacelli says this newer algorithm is actually being unveiled more quickly than initially planned. "The FDA is very keen on us running a trial and the Artificial Pancreas needs a (CGM) sensor that is dosing-worthy," he said. "We were going to wait for a future generation to add in this advanced algorithm, but the FDA was ready for that now."

The FDA has shown keen interest in moving Artificial Pancreas technology forward; remember, the regulatory agency in late 2012 approved final guidance for these AP devices and in Fall 2013 approved the Medtronic 530G that's the first device to include an automatic insulin suspend if glucose levels go too low.

And now, Dexcom plans to begin additional AP trials with the new algorithm being used for dosing, Pacelli says.

We're excited to see this technology moving forward in AP trials, and also being released so customers like us can get share the benefits in real-time!

Disclaimer: Content created by the Diabetes Mine team. For more details click here.

Disclaimer

This content is created for Diabetes Mine, a consumer health blog focused on the diabetes community.
The content is not medically reviewed and doesn't adhere to Healthline's editorial guidelines.
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Archived Comments

DX4|2014-11-18

I remember hearing about a newer algorithm being released to improve accuracy over a year ago. Its great that its finally been released to US customers, I hope it will be released outside the US soon and I look forwards to the g5 (next year hopefully); we first heard about almost two years ago? Whilst dexcom are obviously running their products though a lengthy lifecycle to maximise profits - it feels like they could release newer products faster, Im probably not alone in saying that I'm bored of taking a survival kit with me everywhere I go. phone, wallet, cgm, insulin, sometimes manual test equipment - some people have pumps on top of all of that. Hackers seem to be responding to the diabetes tech industry sluggishness by creating custom products/hacks to bring long talked about prospective tech to t1d patients faster and cheaper

droberts0503|2014-11-18

I haven't really noticed a difference. It's still about 25-30% off when I wake up, often sounds the 55 alarm when I'm nowhere near 55 and generally seems to be about the same as before. It's definitely updated but yet another Dexcom let down for me. I wonder if I'm just cursed with the company.

Ben Cauthren|2014-11-18

Any news on whether or not they plan to release the update for Mac users? Like many others, I'm sure, I have Macs at home and my only access to a PC is a work computer that doesn't allow me to download updates of this sort without administrator access. So we are out of luck in taking advantage of this update.

Matthias|2014-11-18

My results have been pretty favorable. It isn't always in agreement with my fingersticks, but I suspect the fault lies with my Verio IQ meter. The back-to-back testing accuracy is not great there.

Kim|2014-11-18

I just had my doctor update mine after she pulled data at my last appointment. I'm in the same boat as you and am happy they asked if I wanted them to upgrade.

Tom C.|2014-11-18

Mike, I always enjoy reading your postings--very relevant and informative! I have a question about something you wrote in December 2013 about your unexplained high blood sugars while using the t:slim. That was around the time that Tandem recalled defective cartridges. Could the high readings you had be a result of those bad cartridges? I'm considering a t:slim but I'm concerned after reading sporadic reports on the net about unexplained highs similar to what you described. I'm now wondering if all of those incidents are a result of the bad cartridges. Any thoughts?Many thanks,Tom C.

mcityrk|2014-11-18

It might be a bit of a pain, but places like Kinko's/FedEx usually have PCs on hand and rent time for usage. Maybe that is worth checking out--

David|2014-11-18

So cool, thanks Mike. The new algorithm would be quite an upgrade for someone like myself who last used the PLUS. Integrating the older algorithm into the Vibe and Tslim seems like a poor plan, especially for Tandem because by the time the integrated system is approved and launched, the G5 might be out.

Doug|2014-11-19

Ive seen what appears to be better accuracy as well. Ive actually seen the Dexcom match my Freestyle exactly a few times and rarely be more than 10 points or 10% off which is great. I disagree with the comment that Dexcom is "Whilst Dexcom are obviously running their products though a lengthy lifecycle to maximise profits — it feels like they could release newer products faster," Forget FDA - how long do you think it takes a company to design build and produce a complex product like this ? Do you see ANY high tech company produce a totally new product every year ? What companies have the revenue and RandD budget to do that ? I think Ive had a dexcom for 3 years ? Maybe 4 - In that time they have released a smaller transmitter. Then the Gen 4 Platinum and now a FREE software update. Thats pretty good.Lets compare that to Minimed - the 800 lb gorilla in the industry with the largest market share and the largest budgets. The MM sensor is still viewed as the worst in the market place. With few significant updates in the same time. Disclosure - Im also a DXCM stock holder. I wish my Tandem stock was doing as well and DXCM ...

Beth|2014-11-19

Since the Vibe isn't approved yet (and therefore not on the market) I don't understand why they can't upgrade them before shipping. The more I am hearing about the Vibe, the more I think I don't want it! I wouldn't be able to see receiver on my bike handlebars, and wouldn't have the new algorithm. The only benefits would be the waterproofness and one less device to carry - but I think I value the other options more.

David|2014-11-19

@Beth, I don't think Animas can just download the new Dexcom algorithm without a massive re-write of the Vibe. The way Dexcom keeps improving their product every few years means that integrated pumps will constantly be behind the curve. Pump companies may be forced to re-jigger their designs to allow easy and quick upgrading of the Dexcom component. My workaround and ultimate hope is to keep my pump separate from Dexcom via the future G5 smartphone system.

jogger|2014-11-20

I am deciding between T-slim and Medtronic as a new purchase. I;ve tested both. Not sure which way to go. Medtronic sensor is bad. T-slim right now has no sensor, but the hopes of connecting to Dexcom, but right now that is a moot point. Medtronic has the strong history. I'm not so confident of T-slim's performance. Any input from T-slim users who have or have not used the Medtronic pump would be helpful. How is the smart phone an issue between pumps?

Scott Powell|2014-11-21

I have seen dramatically better readings since the 505 update. I still find that my "worst" differences between Dexcom and blood test are in the morning - but it's gone from being sometimes 50+% off to only being 10 - 15% off under the 505 software. At other times during the day, I'm usually off by less than 5%.This is a HUGE improvement for me - I was a long time Abbott Navigator user, and I like everything about the Dexcom better, except the accuracy. I always dosed off of the Navigator, as it was never off by more than about 5 percent (used it for years).It looks to me like the Dexcom is finally getting close to that level of accuracy.Scott

Scott Powell|2014-11-21

p.s. now if we could just get to where the navigator was on only taking a calibration test once every two days, vs. 2 tests per day...Scott

Melissa Lee|2014-11-24

Scott, completely agree about the Abbott Freestyle Navigator. I used it from 2008-2011 and found it to be so much more accurate than any Dexcom product I've used since. I miss it. It was always within 5 mg/dL of my BG.

Scott Powell|2014-11-26

Melissa, if you're using Dexcom, I highly recommend getting the 505 update. Really starting to feel like it's closing the gap. I seldom see readings over 10% off, and many are under 5% off. To me, that's close enough. Granted, that's 5%, not 5 points...but 5% to me is accurate enough. I also don't see a lot of the weirdness the previous version of the software had (i.e. getting ??? when I choose to eat something "bad" and my sugar spikes up, not seeing things like calibrations pushing the Dexcom reading the wrong direction, etc.)Scott

Scott Powell|2014-11-26

p.s. also just to follow up, prior to the 505 update I seldom saw calibrations that were under 10% off, sometimes they'd be as much as 50% off (rare, but probably happened at least several times a month). Those seem to be a thing of the past.Scott

CSweet|2014-12-08

I have a question about the comments: "On top of that, two new pumps that will integrate the Dexcom CGM that are undergoing FDA review now won't be compatible with this new algorithm... As a result, Pacelli tells us t:slimmers and Animas pumpers who get either integrated pump will either have to buy a separate Dexcom G4 receiver to have the advanced algorithm or they'll have to wait for the second generation of these integrated devices that will include the yet-to-be-filed G5 sensor.".Does this mean we CAN simultaneously have both versions of the G4 algorithm? The newer one on the handheld receiver and the older one running on the integrated/future integrated pump? Do I have that right? I don't mind 2 devices.

MikeH|2014-12-09

Yep, that's what that would mean, C -- you'd have an updated algorithm used by the G4 receiver, and then what's integrated into the ibe or t:slim would be the non-updated G4 algorithm.

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